The present invention relates to a method of manufacturing extruded seamless hollow materials, in particular, to a manufacturing method contrived to reduce the deviation in thickness at the beginning of extrusion.
The manufacturing method of conventional seamless hollow materials will be explained by FIG. 6. The extrusion dies 2 is provided on the extruding side of container liner 1 and a hollow billet "a" is inserted into the container liner 1. The mandrel 3 is inserted into the billet "a" adjusting the sight to the center of extrusion hole 21 of dies 2 and the hollow billet "a" is pressurized by ram 4 to be extruded.
The wall thickness of the extruded hollow materials is determined by the clearance between the outer diameter of mandrel 3 and the extrusion hole 21 of dies 2. But, when starting in the extrusion by pressurizing the billet "a", the tip of mandrel 3 is not accurately kept at the center of extrusion (center of extrusion hole 21 of dies 2) due to the swings etc. Therefore, there has been a drawback that the deviation occurs in the wall thickness of the extruded hollow materials at the beginning of extrusion.
The purpose of the invention lies in providing a method of manufacturing extruded seamless hollow materials wherein the occurrence of such deviation in thickness is lessened.